Magnesium-base alloy



United States Patent 3,183,083 MAGNESIUM-BASE ALLOY George S. Foerster, Midland, Mich, assiguor to The Dow Chemical Company, Midland, Micln, a corporation of Delaware No Drawing. Filed Feb. 24, 1961, Ser. No. 91,327 7 Claims. (Ci. 75-168) Percent Zinc 7 to 16 Zirconium 0.1 to 1.0 Rare earth met-a1 1 to 8 Magnesium, substantially the balance.

Generally, as the amount of zinc is increased, the amount of rare earth element should be increased if the workability and the optimum strength properties are to be retained. In a more desired range of compositions the alloy contains 9 to 12 percent zinc, 2 to 4 percent rare earth elements, 0.4 to 0.8 percent zirconium, the balance being substantially magnesium. The optimum alloy comingredients in proper proportions or by using hardeners of magnesium alloys containing the alloy constituents. Protection from oxidation during alloying is effected by the use of a magnesium chloride-free saline flux as in conventional alloying of magnesium. The molten alloy may be flux refined, if desired, by stirring the alloy with additional flux. The so-refined metal is allowed to settle and then is separated from the flux 'as by decanting into' a suitable casting mold, e.g., a round mold for extrusion stock.

In extruding the cast metal, it is desirable first to scalp the cast metal so as to present a smooth clean surface to the extrusion die. The clean extrusion stock is heated to a suitable temperature, e.'g., about 600? to 800 F. The heated metal is then extruded in a conventional metal extrusion press.

The following examples are given to illustrate the present invention but are not to be construed as limiting the invention thereto.

EXAMPLE Various alloy compositions were cast into billets 3 inches in diameter, scalped to 2% inch diameter, cut into 4 inch lengths, heated to between 600 and 800 F. and extruded from the 3 inch container of a 500 pound press into a x inch strip until a butt length of inch remained. The butt was sheared after each push and the strip tested for properties. The alloy compositions, extrusion conditions and compression yield strengths are listed in Table I.

Table I Alloy Composition, By

Weight Ram Extrusion Test Pressure, Speed, OYS, p.s.i.

Tons ft./miu. Percent Percent Percent Zn Zr MM 6 0. 7 2 450 5 40,000. 6 0.7 2 250 5 32,000. 6 0. 7 450 5 42,000. 6 0. 7 450 15 41,000. 6 0. 7 250 5 30,000. 15 .7 450 3 4A3fi000. m t

K 0y cou no lg gg be extruded 15 250 5 without hot shorting.

1 Balance magnesium. CYS=compression yield strength. hot shorting=craeking or tearing. MM=miseh metal.

position is 9 percent zinc, 0.8 percent zirconium, 2 to 3 percent rare earth elements. Thorium in amounts of 0.5 to 8 percent of the alloy may replace part or all of the rare earth metal without significant alteration in properties.

Rare earth metals suitable for use in preparing the present alloy are Ce, La, Pr, Nd, or misch metal (a mixture of rare earth metals). Misch metal containing from to 80 percent of cerium, the balance being rare earth metal and up to 5 percent of non-rare earth metal, is the preferred rare earth metal ingredient of the alloy. Any of the foregoing rare earth metals may be used alone or in any combination in compounding the alloy.

The alloy may be made in the desired proportions according to the invention by melting together the alloying The results listed in Table I show that the alloy of the invent-ioin exhibits a high level of compression yield strengths over a wide range of extrusion pressures and speeds, whereas similar alloys outside the scope of the invention are much more sensitive to changes in extrusion conditions and exhibit lower compression yield strengths.

To further illustrate the relative insensitivity of the present alloy to changes in extrusion conditions several embodiments of the alloy and a comparison alloy were each extruded in a similar manner to that described hereinabove except that the extrusion container temperature and the temperature of the scalped extrusion billet were carefully controlled and maintained at preselected temperatures. The billets were each subjected to 400 tons 3 push (maximum pressure) and extruded at a speed of 5 feet per minute. The resulting extrusions were tested for compression yield strength. The results of the tests are listed in Table II.

Table II 5 Alloy Compsiti0n, By

weight Extrusion Test 'Iempera- OYS, ture, F. p.s.i. Percent Percent Percent 1 0 Zn Zr Th 1 Balance mag-nesium.

. I Among the advantages of the alloy of the 1nvent1on 1s the relative insensitivity of the alloy to changes in extrusion conditions, thus reducing or eliminating the necessity for constant sampling, testing and rejection portions of extrusions failing to meet specifications because of diiierences between the nose, middle, and butt of the extrusion.

I claim: 1. A magnesium-base alloy which comprises by weight: from 9 to about 15 percent zinc, from about 0.1 to about 1.0 percent zirconium, from about 1 to about 8 percent rare earth metal, the balance being substantially magnesium.

2. An extruded magnesium metal article consisting of, by weight, from 7 to 16 percent zinc, from about 0.1 to about 1.0 percent zirconium, from about 1 to about 8 percent rare earth metal, and the balance being substantially magnesium; and said article having a compression yield strength of at least 42,000 pounds per square inch.

3. An extruded magnesium metal article consisting of, by weight, from about 7 to about 16 percent zinc, from about 0.1 to about 1.0 percent zirconium, from about 1 to about 8 percent rare earth metal, and the balance being substantially magnesium; and said article having a compression yield strength of at least 37,000 pounds per square inch.

4. An extruded magnesium metal article consisting of, by Weight, from 7 to about 16 percent zinc, from about 0.1 to about 1.0 percent zirconium, from about 1 to about 8 percent rare earth metal, and the balance being substantially magnesium; and said article having a compression yield strength of at least 34,000 pounds per square inch.

5. The alloy as in claim 1 in which part of the rare earth metal content is replaced by thorium.

6. A magnesium-base alloy which comprises: from 9 to 112 percent of zinc, from 0.4 to 0.8 percent of zirconium, from 2 to 4 percent of rare earth metal, the balance being substantially magnesium.

7. A magnesium-base alloy which comprises: about 9 percent of zinc, about 0.7 to 0.8 percent zirconium, about 2 to 3 percent of rare earth metal, the balance being substantially magnesium.

References Cited by the Examiner UNITED STATES PATENTS 2,720,310 10/55 Yack et al. 207-10 2,750,288 6/56 Jessup et al. -168 2,806,596 9/57 Dodds et al. 207--10 2,829,973 4/58 Jessup et a1. 75-168 FOREIGN PATENTS 205,975 1/57 Australia.

DAVID L. RECK, Primary Examiner.

MARCUS U. LYONS, RAY K. WINDHAM, ROGER L. CAMPBELL, Examiners. 

1. A MAGNESIUM-BASE ALLOY WHICH COMPRISES BY WEIGHT: FROM 9 TO ABOUT 15 PERCENT ZINC, FROM ABOUT 0.1 TO ABOUT 1.0 PRECENT ZIRCONIUM, FROM ABOUT 1 TO ABOUT 8 PERCENT RARE EARTH METAL, THE BALANCE BEING SUBSTANTIALLY MAGNESIUM. 